Empleo de la GnRH para el tratamiento de quistes ováricos

Además de ser empleada para inducir y sincronizar el estro y/o la ovulación, la GnRH puede ser usada para el tratamiento de quistes ováricos en vacas. Los quistes foliculares por lo general son tratados mediante la administración de análogos sintéticos de la GnRH aprobados para su uso en vacas lecheras lactantes (Fricke, 2000). El tratamiento con GnRH induce la luteinización más que la ovulación del quiste folicular, lo que resulta en la formación de un quiste luteal (Garverick, 1997; Fricke, 2000), cuya regresión puede ser inducida mediante la administración de PGF2α (Nanda et al., 1988). La administración de GnRH a vacas con quistes foliculares benignos a menudo induce la ovulación de un folículo dominante de crecimiento normal más que del quiste mismo (Garverick, 1997; Fricke, 2000).

El tratamiento ideal para quistes ováricos debería ser efectivo para todos los tipos de éstos. El protocolo Ovsynch para sincronizar la ovulación en vacas lecheras lactantes usa tanto inyecciones de GnRH como de PGF2α (Pursley et al,. 1995, 1997a), y puede ser un tratamiento efectivo para los quistes ováricos. En un estudio realizado por Fricke (2000) en vacas lecheras lactantes, el tratamiento con Ovsynch indujo la ovulación de un folículo y no del quiste presente al momento de la segunda inyección de GnRH en el 73% de las vacas, de las cuales el 37% concibieron después de IATF. Estos resultados sugieren que el Ovsynch puede ser el tratamiento de elección para quistes ováricos en vacas lactantes (Fricke, 2000).

De acuerdo con Rubio (2005), cuando se administran dosis de GnRH de 0.1 a 0.5 mg para el tratamiento de quistes foliculares, ocurre la luteinización sin ovulación, y cuando la dosis oscila entre 0.5 y 1.5 mg se produce ovulación y luteinización, con un 90% de vacas que responden presentando un celo fértil 18 a 24 días después.

CONCLUSIONES

En la actualidad, en la hembra bovina la GnRH se usa principalmente para inducir y/o sincronizar el estro y/o la ovulación para facilitar la IATF, al igual que para el tratamiento de quistes ováricos.

Los diferentes protocolos para la inducción y/o sincronización del estro y/o de la ovulación que usan GnRH también incluyen la aplicación de PGF2α. Estos protocolos pueden aplicarse en cualquier etapa del ciclo estrual, aunque la eficacia de la GnRH para inducir la ovulación se ve afectada por la etapa de desarrollo folicular al momento de su aplicación. La GnRH induce la ovulación de folículos ≥10 mm de diámetro durante la fase de crecimiento folicular.

En los protocolos que usan GnRH, la primera inyección de esta hormona programa el crecimiento folicular en vacas cíclicas e induce la ovulación en vacas anéstricas. La PGF2α el día 7 causa la lisis de cualquier cuerpo lúteo presente y de los folículos luteinizados como resultado de la GnRH. La segunda inyección de GnRH el día 9 induce la ovulación de los folículos dominantes que fueron pre- programados por la primera inyección de GnRH. Estos protocolos aseguran una mayor sincronía en la oleada de LH, con lo que se sincroniza el desarrollo folicular y la luteólisis, y han sido utilizados con tasas de gestación aceptables en ganado Bos taurus productor de carne y lechero, mas no en ganado Bos indicus.

Existe un protocolo que añade progesterona natural al tratamiento de GnRH + PGF2α, y que resulta en especial útil en vacas anéstricas, ya que la progesterona asegura que la mayoría de las hembras ovulen, que se induzca la aparición de ciclos estruales normales, y que se evite la aparición de estros tempranos.

Por otro lado, la GnRH puede ser usada para el tratamiento de quistes foliculares, induciendo su luteinización para formar un quiste luteal que puede ser lisado usando PGF2α.

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